Preventing Preterm Birth With Probiotics

Preterm birth (PTB) is defined as the birth of a baby before the completion of 37 weeks gestation in the womb. It is the major cause of infant mortality particularly during the first month of life. Approximately 75 per cent of babies who die during the first 28 days of life are born before 37 weeks gestation. Survivors of PTB are at increased risk of long-term disabilities such as cerebral palsy, sight and hearing impairment, learning and behavioural problems, epilepsy, and hospital readmissions. Even late preterm births, defined as PTB at 34--36 weeks gestation, which account for 70% of all preterm births in England and Wales, are at increased risk of death and disability compared with babies born at term. Although the prevalence of adverse long--term outcome is highest among children born at the earliest gestational ages, the much higher number of births at 34--36 weeks of gestation compared with earlier gestations means that this group of children makes a major contribution to the number of children adversely affected. PTB and its consequences can have negative emotional and psychosocial impacts on parents and families.

In addition to its impact on individuals and families, the financial consequences for the public sector of caring for children born preterm are significant. The cost of care up to the age of 18 for children born preterm has been estimated to exceed £3 billion per year in England and Wales at 2006 prices. It has been estimated that a hypothetical intervention that delayed PTB by 1 week across all gestational age categories would reduce the public sector cost of PTB by £1 billion annually.

About one third of PTBs occur because early delivery is indicated due to complications in the mother or the unborn baby (fetus); the remaining two thirds occur spontaneously. The rate of PTB has increased by 19% from 1990 to 2010 in developed countries. At the same time, there has been a marked improvement in the survival rates of PTBs but a similar reduction in adverse outcomes has not been seen. Thus, the absolute numbers of individuals adversely affected is increasing.

Infection within the womb (intrauterine infection) is strongly associated with spontaneous PTB. The commonest pathway for intrauterine infection is the ascent of unhealthy bacteria from the vagina and cervix into the womb. Bacterial vaginosis (BV), in which the normally dominant healthy bacteria in the vagina (lactobacilli) are replaced with unhealthy bacteria, is strongly associated with PTB. Lactobacilli, principally the strains that produce higher levels of the chemical hydrogen peroxide, appear to protect against BV and reduce the risk of PTB.

Despite substantial evidence linking BV with PTB, the results of trials of antibiotic treatment of BV in pregnancy have not produced clear evidence of benefit. The reason for this might be that it is not the eradication of unhealthy bacteria that is required but rather the replacement of unhealthy bacteria with the normally dominant lactobacilli. One way of achieving this could be by administering lactobacilli-containing capsules (probiotics) to pregnant women. Oral probiotics taken during pregnancy may directly alter the vaginal bacteria and in so doing protect the cervical opening from ascending infection.

The investigators have formally reviewed the medical literature on the use of probiotics to prevent PTB. There is some evidence from medical trials which suggests that probiotics taken during pregnancy can reduce the risk of PTB but the trials have either been too small or of poor quality for the results to be conclusive. The results of an observational study on nearly 19,000 pregnant women suggested that probiotic- containing foods reduced the risk of spontaneous PTB.

The best way to determine whether probiotics can reduce the risk of PTB is by performing a type of study called a double-blind, randomised controlled trial (RCT). In such a trial, the participants are allocated to receive either probiotic supplements or dummy (placebo) supplements. The allocation to a particular supplement is purely by chance (random) and neither the participants nor the researchers know the allocation of any participant until the end of the trial (double-blind). Then, by looking at the difference in the rate of PTB between the groups it would be possible to say whether probiotics can reduce the rate of PTB. The investigators have estimated that an RCT that could detect a useful difference in the rate of PTB between the two groups would require the participation of approximately 10,000 women and cost several million pounds. Given that approximately 20,000 deliveries occur annually in inner North East London alone, there are sufficient women in this region who would be eligible for participation in such a RCT. However, the willingness of women to participate in and complete such a trial is unknown.

A small, pilot trial is required to determine what proportion of pregnant women would participate in a probiotics and PTB trial and the proportion that would complete the study. The proposal here, the PrePro trial, is designed to gather these data which will inform the feasibility, planning and execution of a large RCT looking at the effects of probiotics on PTB.

Potential risks and benefits of probiotics The World Health Organisation defines probiotics as live micro-organisms that confer a health benefit on the host when administered in adequate amounts. They can displace and kill pathogens, and modulate the immune response by interfering with the inflammatory cascade that can cause preterm labour. Administration of probiotics by mouth or intravaginally is safe and effective in reducing the incidence of or treating urogenital infections. There is no evidence of adverse consequences for mothers or their infants as a result of probiotic exposure during pregnancy. Acceptability of and compliance with daily ingestion of probiotic or placebo for a few weeks during mid-pregnancy was found to be high. The particular probiotic strains proposed for this study have been shown to be acceptable to and safe in pregnant women, and can colonise the vagina within 4 weeks of commencing oral intake.

A large intervention trial of ingesting oral capsules from early pregnancy to the end of gestation has not been performed in the UK. For such a trial to be successful, it is essential to gather data that will inform its feasibility, planning and execution. PrePro is designed to provide these data. This trial will be conducted in compliance with the study protocol, relevant regulations, and the MRC Guidelines for Good Clinical Practice (GCP).